To diagnose preterm labor, your doctor will review your symptoms and medical history. Your doctor may do or recommend one or more of the following:

Pelvic Exam

The pelvic exam is done to see if your cervix has begun to dilate or to thin. If dilation has begun, you may be in preterm labor. Dilation is measured in centimeters from 0-10. Birth usually occurs after the cervix has dilated to 10 centimeters. Thinning of the cervix is called effacement. It is reported as a percent. If you are 50% effaced, your cervix has thinned to half of its original thickness. When you reach 100% effaced, the cervix is completely thinned and ready for a vaginal delivery.

Sometimes, the length of the cervix is assessed by an ultrasound measurement.

Tocometer

A tocometer is a machine that measures uterine contractions. A tocometer is a monitoring device that tracks the frequency and length of contractions. Over a short period of time, a pattern emerges that can help your doctor with a diagnosis.

Fetal Fibronectin

During the pelvic exam, your doctor may swab your cervix to test for fetal fibronectin (fFN). fFN acts as a glue to attach the amniotic sac to the lining of the uterus. It is normal for fFN to be in cervical secretions for the first 22 weeks of pregnancy. However, if fFN is present in the outer cervix beyond weeks 22-34, this glue may be breaking down earlier than it should. fFN may be a sign of impending preterm labor.

The presence of fFN (positive test result) is not a good predictor of whether you are at risk of preterm birth. However, the absence of fFN (negative test result) is a good predictor that you are not at risk of a preterm birth at this time. Your pregnancy is likely to continue for at least another two weeks.

Ultrasound

An ultrasound may also be done. This test uses sound waves to create an image of your uterus, the fluid around the baby, and the baby.

Revision Information

This content is reviewed regularly and is updated when new and relevant evidence is made available. This information is neither intended nor implied to be a substitute for professional medical advice. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with questions regarding a medical condition.

How do health care providers diagnose preterm labor?
National Institute of Child Health and Human Development website. Available at:
http://www.nichd.nih.gov/health/topics/preterm/conditioninfo/Pages/diagnosed.aspx. Updated November 30, 2012. Accessed April 23, 2013.

Preterm labor and birth. March of Dimes website. Available at:
http://www.marchofdimes.com/pregnancy/preterm%5Findepth.html. Updated September 2012. Accessed April 23, 2013.

Preterm labor. The American College of Obstetricians and Gynecologists website. Available at:
http://www.acog.org/~/media/For%20Patients/faq087.pdf?dmc=1&ts=20130423T0923201528. Accessed April 23, 2013.

Uterine contractions. Center for Experiential Learning, Quillen College of Medicine, East Tennessee State University website. Available at:
http://utilis.net/fhm/2426.htm. Accessed April 23, 2013.